The present disclosure relates, in various exemplary embodiments, to electronic devices, including microelectronic devices, and materials suitable for use in such devices. More specifically, the present disclosure relates to devices that incorporate siloxy/metal oxide hybrid compositions or materials in the dielectric layers for such devices as thin film transistors.
Thin film transistors are fundamental components in modern-age electronics, including, for example, sensor, imaging, and display devices. Thin film transistor circuits using current mainstream silicon technology may be too costly, particularly for large-area device applications such as backplane switching circuits for displays like active matrix liquid crystal monitors or televisions, where high switching speeds are not essential. The high costs of silicon-based thin film transistor circuits are primarily due to the capital-intensive silicon fabrications as well as the complex high-temperature, high-vacuum photolithographic fabrication processes under strictly controlled environments.
Because of the cost and complexity of fabricating silicon-based thin film transistor circuits using conventional photolithography processes, there has been an increased interest in plastic thin film transistors which can potentially be fabricated using solution-based patterning and deposition techniques, such as spin coating, solution casting, dip coating, stencil/screen printing, flexography, gravure, offset printing, ink jet-printing, micro-contact printing, and the like, or a combination of these processes. Such processes are generally simpler and more cost effective compared to the complex photolithographic processes used in fabricating silicon-based thin film transistor circuits for electronic devices. To enable the use of these solution-based processes in fabricating thin film transistor circuits, solution processable materials are therefore required.
Most of the current materials research and development activities for plastic thin film transistors has been devoted to semiconductor materials, particularly solution-processable organic and polymer semiconductors. On the other hand, other material components such as solution processable dielectric materials have not been receiving much attention.
For plastic thin film transistor applications, it is desirable to have all the materials be solution processable. It is also highly advantageous that the materials be fabricated on plastic substrates at a temperature of less than about 200° C., and particularly less than about 150° C. The use of plastic substrates, together with flexible organic or polymer transistor components can transform the traditional thin film transistor circuits on rigid substrates into mechanically more durable and structurally flexible plastic thin film transistor circuit designs. Flexible thin film transistor circuits will be useful in fabricating mechanically robust and flexible electronic devices.
Other than solution processable semiconductor and conductor components, solution processable dielectric materials are critical components for the fabrication of plastic thin film transistor circuits for use in plastic electronics, particularly flexible large-area plastic electronics devices.
Generally, the dielectric layer which serves as the gate dielectric in a thin film-transistor should i) be a smooth uniform layer without pinholes, ii) have a high dielectric constant to enable the thin film transistor to operate at lower voltages, and iii) have no adverse effects on the transistor's performance. Additionally, for flexible integrated circuits on plastic substrates, the dielectric layer should be prepared at temperatures that would not adversely affect the dimensional stability of the plastic substrates, i.e., generally less than about 200° C., preferably less than about 150° C.
A wide variety of organic and polymer materials, including polyimides [Z. Bao, et al. J. Chem. Mater. 1997, Vol. 9, pp 1299.], poly(vinylphenol) [M. Halik, et al. J. Appl. Phys. 2003, Vol 93, pp 2977.], poly(methyl methacrylate) [J. Ficker, et. al. J. Appl. Phys. 2003, Vol 94, 2638.], polyvinylalcohol [R. Schroeder, et. al. Appl. Phys. Lett. 2003, Vol 83, pp 3201.], poly(perfuoroethylene-co-butenyl vinyl ether) [J. Veres, et al. Adv. Funct. Mater. 2003, Vol 13, pp 199.]], and benzocyclobutene [L. -L. Chua, et. al. Appl. Phys. Lett. 2004, Vol 84, 3400.], have been studied as dielectric layers. These materials, however, do not generally meet all the economic and/or functional requirements of low-cost thin film transistors. In particular, most of the organic or polymer dielectric materials generally have low dielectric constants, and thus cannot enable low-voltage electronic devices.
Therefore, it is desirable to provide a dielectric material composition that is solution processable and which composition can be used in fabricating the gate dielectric layers of thin film transistors It is equally desirable to provide a dielectric material that will permit easy fabrication of a gate dielectric layer for thin film transistors by solution processes, that is pinhole free, has a high dielectric constant, and exhibits electrical and mechanical properties that meet the device physical and performance requirements. It is also desirable to provide a material for fabricating the dielectric layer for thin film transistors that can be processed at a temperature compatible with plastic substrate materials to enable fabrication of flexible thin film transistor circuits on plastic films or sheets.